Method and device for monitoring the direction of rotation of a piston engine

ABSTRACT

A method and device for detecting the rotation direction of a piston engine, internal combustion engine or piston compressor. The piston engine includes at least one cylinder, a piston movable back and forth in the cylinder, a cylinder chamber formed inside the cylinder which is delimited by an inner cylinder wall and the piston, an inlet channel opening into the cylinder chamber via at least one inlet valve, an outlet channel opening into the cylinder chamber via at least one outlet valve, and at least one triggerable throttling device situated in the inlet channel. To detect the rotation direction in a reliable, timely, and simple manner, the pressure prevailing in the inlet channel is measured when a rotary motion is detected, compared with a predefinable threshold value, and the rotation direction is determined based on the comparison result, the throttling device being closed at least for the pressure measurement time.

FIELD OF THE INVENTION

The present invention relates to a method for detecting the direction ofrotation of a piston engine, in particular of an internal combustionengine or of a piston compressor. The present invention also relates toa device for detecting the direction of rotation of a piston engine.Furthermore, the present invention relates to a control unit forcontrolling and/or regulating a piston engine. The present inventionfinally also relates to a computer program which is able to run on acomputer, in particular on a microprocessor.

BACKGROUND INFORMATION

To ensure safe operation of a piston engine, it must be made sure thatthe piston engine rotates in a predefined direction. A wrong directionof rotation may be triggered in the case of an internal combustionengine, for example, by an erroneous ignition angle output and injectionoutput of a control unit of the engine at start or by a wrong directionof rotation during start as may occur, for example, when the clutch isengaged while the vehicle is rolling backward with a forward gearengaged.

A wrong direction of rotation may result, in the case of an internalcombustion engine, for example, in a subsequent start attempt remainingfruitless for some time due to the excessively rich fuel-air mixture.Furthermore, in the event of a wrong direction of rotation there is therisk of damage or destruction of devices in the inlet channel such as,for example, the intake manifold, the throttling device, or a flowmeter.Should the internal combustion engine rotate in the wrong direction,uncontrolled combustion could occur in a cylinder chamber. The inletvalve of the cylinder chamber would be open after the combustion and thehot exhaust gases would enter the inlet channel via the open inletvalve. The devices in the inlet channel could become damaged ordestroyed due to a return stroke caused by the uncontrolled combustionin the cylinder and by the high exhaust gas temperatures.

A control unit for detecting the direction of rotation of an internalcombustion engine of the above-mentioned type is discussed, for example,in German patent document no. 199 33 845, where the rotation of acamshaft of the internal combustion engine is detected by an absolutephase angle sensor, such as is discussed, for example, in German patentdocument no. 197 22 016. It is then determined, by querying the absolutephase angle, whether the signal is monotonously increasing ormonotonously decreasing. The direction of rotation is determined fromthis information by a control unit.

In the past, reliable absolute phase angle sensors using themagnetoresistive effect and the Hall effect have been relatively complexcomponents that included at least one control unit and a plurality ofsensors.

SUMMARY OF THE INVENTION

An object of the exemplary embodiment and/or exemplary method of thepresent invention is to detect the direction of rotation of a pistonengine in a reliable, timely, and simple manner.

The exemplary embodiment and/or exemplary method of the presentinvention relates to a method for detecting the direction 6 f rotationof a piston engine, in particular of an internal combustion engine or ofa piston compressor. The piston engine includes at least one cylinder; apiston movable back and forth in the cylinder; a cylinder chamber formedinside the cylinder, which is delimited by an inner cylinder wall andthe piston; an inlet channel, which opens into the cylinder chamber viaat least one inlet valve; an outlet channel, which opens into thecylinder chamber via at least one outlet valve; and at least onetriggerable throttling device situated in the inlet channel.

The exemplary embodiment and/or exemplary method of the presentinvention also relates to a device for detecting the direction ofrotation of a piston engine, having at least one cylinder; a pistonmovable back and forth in the cylinder; cylinder chamber formed insidethe cylinder, which is delimited by an inner cylinder wall and thepiston; an inlet channel, which opens into the cylinder chamber via atleast one inlet valve; an outlet channel, which opens into the cylinderchamber via at least one outlet valve; at least one triggerablethrottling device situated in the inlet channel; and a control unit forcontrolling and/or regulating the piston engine.

Furthermore, the exemplary embodiment and/or exemplary method of thepresent invention relates to a control unit for controlling and/orregulating a piston engine, having at least one cylinder; a pistonmovable back and forth in the cylinder; a cylinder chamber formed insidethe cylinder, which is delimited by an inner cylinder wall and thepiston; an inlet channel, which opens into the cylinder chamber via atleast one inlet valve; an outlet channel, which opens into the cylinderchamber via at least one outlet valve; and at least one triggerablethrottling device situated in the inlet channel.

The exemplary embodiment and/or exemplary method of the presentinvention finally also relates to a computer program which is able torun on a computer, in particular on a microprocessor.

Based on a method described herein, the exemplary embodiment and/orexemplary method of the present invention provides that the pressureprevailing in the inlet channel be measured while the piston engine isrotating and compared with a predefinable threshold value, and thedirection of rotation of the piston engine then be determined via theresult of the comparison. A triggerable throttling device is closed atleast for the time of the pressure measurement to isolate the area ofthe cylinder chamber and the inlet channel from upstream systems such asa turbocharger or a pressure (or vacuum) accumulator, for example.

On this basis appropriate countermeasures may then be taken to preventdamage to the piston engine. Such countermeasures include, for example,stopping the piston engine in the event of a wrong direction ofrotation. This may be accomplished, for example, by interrupting thesupply of fuel-air mixture or interrupting the ignition.

The operating principle of a piston engine is that a mostly gaseoussubstance is aspirated into the internal cylinder chamber via an openinlet valve in an intake phase. This is accomplished by the fact thatthe volume of the internal cylinder chamber is enlarged by anappropriate movement of the piston. The inlet valve is then closed, thesubstance in the internal cylinder chamber is compressed by a subsequentpiston movement in the opposite direction, and then expelled again viaan outlet valve. In an internal combustion engine, the mixture isignited during or after the compression of a fuel-air mixture and thenexpelled via the outlet valve. In a piston compressor, the gaseoussubstance aspirated via the inlet valve is expelled during or after thecompression via the outlet valve. A partial vacuum may thus be producedin a body connected to the inlet channel or an overpressure may beproduced in a body connected to the outlet channel.

The piston engine has an intended direction of rotation due to this modeof operation. If it is attempted to operate the piston engine in theopposite direction, the functions of the inlet and outlet valves arereversed. This would mean that the substance aspirated via the outletchannel and compressed is discharged into the inlet channel via theinlet valve. A pressure that is higher than that in the piston engineoperated in the intended direction of rotation will thus prevail in theinlet channel (and thus also in the cylinder chamber) at this point intime. A threshold value may thus be specified for the pressureprevailing in the inlet channel. The pressure in the inlet channel willbe less than the threshold value when the piston engine is operated inthe intended direction of rotation. However, if the threshold value isexceeded, this would indicate that the piston engine is being operatedin the wrong direction of rotation.

According to an exemplary embodiment of the present invention, thethreshold value may be determined as a function of a pressure prevailingin the outlet channel. The exemplary method of the present inventionfollows the observation that in a piston engine operated in the intendeddirection of rotation, the pressure in the inlet channel is at no timehigher than that in the outlet channel. This is, however, possible inthe event of a direction of rotation in the opposite direction.Consequently, the instantaneous direction of rotation may be determinedusing this criterion.

In an exemplary method, in a piston engine such as an internalcombustion engine, the threshold value may be determined as a functionof an ambient pressure and an exhaust gas counterpressure. The pressurein the outlet channel may thus be approximated by modeling in a simplemanner.

The threshold value, which is necessary for determining the direction ofrotation, is advantageously described by a predefinable maximum pressurespecific to the piston engine. The maximum value may be determined as afunction of the engine type prior to determining the direction ofrotation and saved in a memory location in a memory of a control unitfor the piston engine provided for this purpose. In this way, both thepressure measurement in the outlet channel and the measurement ormodeling of the ambient pressure and the exhaust gas counterpressure maybe omitted.

As a different approach to achieving the object of the exemplaryembodiment and/or exemplary method of the present invention it isproposed, based on the device of the above-mentioned type, that thedevice include: an arrangement, apparatus or structure for measuring arotation speed; an arrangement, apparatus or structure for triggeringthe throttling device; and an arrangement, apparatus or structure formeasuring the pressure in the inlet channel when the throttling deviceis closed; and that the control unit cause the throttling device toclose when a rotary motion of the piston engine is detected, measure thepressure in the inlet channel after a predefinable measuring period,compare the measured pressure with a predefinable threshold value, anddetermine the direction of rotation of the piston engine on the basis ofthe result of the comparison.

According to an exemplary embodiment of the present invention, it isproposed that the device have an arrangement, apparatus or structure,for example, a pressure sensor, for measuring the pressure in the outletchannel. The pressure prevailing in the outlet channel may be used as athreshold value for the comparison with the pressure prevailing in theinlet channel and thus for the determination of the direction ofrotation. The direction of rotation is then determined by comparison ofthe pressure in the inlet channel with the pressure in the outletchannel.

According to an exemplary embodiment of the present invention, it isproposed that the device have an arrangement, apparatus or structure formodeling the exhaust gas counterpressure and an arrangement, apparatusor structure for measuring the ambient pressure. On the basis of theambient pressure and the exhaust gas counterpressure, the pressureprevailing in the outlet channel and thus also the threshold value maybe determined approximately in a simple manner. The threshold value isthen determined from the sum of these two pressures.

The control unit advantageously includes an arrangement, apparatus orstructure, for example, an electrical memory element, for storing amaximum pressure specific to the piston engine. The maximum pressure isdetermined prior to detecting the direction of rotation as a function ofthe piston engine type, stored in the memory element, and retrieved whenneeded as a threshold value for determining the direction of rotation.This embodiment therefore requires no arrangement, apparatus orstructure for measuring the ambient pressure, the exhaust gascounterpressure, or the pressure in the outlet channel.

The pressure measuring arrangement, apparatus or structure in the inletchannel may include a digital pressure switch which triggers a switchingoperation when the pressure exceeds or drops below the threshold value.On the basis of the output signal of the pressure switch, it may then bedetermined whether the piston engine is moving in the right direction ofrotation.

As a further approach to achieving the object of the exemplaryembodiment and/or exemplary method of the present invention, it isproposed, on the basis of the control unit of the above-mentioned type,that the control unit detect a rotary motion of the piston engine;control the position of the throttling device; and when a rotary motionof the piston engine is detected, cause the throttling device to close,measure the pressure in the inlet channel after a predefinable measuringperiod, compare this pressure with a predefinable threshold value, anddetermine the direction of rotation of the piston engine on the basis ofthe result of the comparison.

Implementation of the exemplary embodiment and/or exemplary method ofthe present invention in the form of a computer program is of particularsignificance. The computer program may be run on a computer, on amicroprocessor in particular, and is suitable for carrying out orperforming the exemplary method according to the present invention. Inthis case, the exemplary embodiment and/or exemplary method of thepresent invention is thus implemented by the computer program, so thatthis computer program represents the exemplary embodiment and/orexemplary method of the present invention in the same way as the methodwhich the computer program is suitable for carrying out. The computerprogram may be stored on a memory element. A random-access memory, aread-only memory, or a flash memory may be used in particular as amemory element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first exemplary embodiment of a device according to thepresent invention.

FIG. 2 shows a second exemplary embodiment of a device according to thepresent invention.

FIG. 3 shows a flow chart of an exemplary method according to thepresent invention.

DETAILED DESCRIPTION

FIG. 1 shows a piston engine as an internal combustion engine 1 having acontrol unit 12 for determining the direction of rotation of internalcombustion engine 1. Internal combustion engine 1 includes a cylinder 3in whose internal cylinder chamber a piston 2 is movable back and forth.An inlet valve 5, an outlet valve 6, and an injection nozzle 9 forinjecting fuel, and a spark plug 10 for igniting the fuel-air mixtureare located on the side of cylinder 3 opposite to piston 2. Insidecylinder 3, a cylinder chamber 4, which in the exemplary embodiment ofFIG. 1 is a combustion chamber, is delimited by an inner cylinder wall,piston 2, as well as inlet valve 5 and outlet valve 6.

An inlet channel 7 opens into combustion chamber 4 via inlet valve 5. Athrottling device 11, which is triggerable by a control unit 12 via acontrol line 16, is mounted in inlet channel 7. Furthermore, a pressuremeasuring device 13, which may be a pressure sensor, is located in inletchannel 7. Device 13 a supplies the measured pressure values to controlunit 12 via a line 14.

An outlet channel 8 opens into combustion chamber 4 via outlet valve 6.A further pressure measuring device 19, which is also a pressure sensor,is situated in outlet channel 8. The values measured by device 19 arerelayed to control unit 12 via a line 18.

Control unit 12 includes an arrangement, apparatus or structure fordetecting the direction of rotation of engine 1. For this purpose,control unit 12 receives information about the rotational speed of theengine via a further line 15, which is accomplished, for example, byquerying a marked transducer disk which is attached to a crankshaft ofengine 1 in a rotationally fixed manner and subsequently evaluating thequeried values via control unit 12. Finally, control unit 12 suppliesthe direction of rotation detected to a higher-level control unit (notillustrated) via control line 17. As an alternative or additionally, ifa wrong direction of rotation is detected, control unit 12 may alsoprovide the necessary countermeasures, which may be transmitted toengine 1 via line 17. The countermeasures include, for example, shuttingdown engine 1 by cutting off the fuel supply via injector 9.

If inlet valve 5 is open and outlet valve 8 is closed, a lower pressureprevails in internal cylinder chamber 4 and in inlet channel 7 than inoutlet channel 8 as piston 2 moves downward. The partial vacuumaspirates air or a fuel-air mixture into combustion chamber 4 ofcylinder 3. The pressures in inlet channel 7 and in outlet channel 8 aremeasured by pressure measuring devices 13 a and 19, and the valuesdetermined are supplied to control unit 12. In the example illustrated,the direction of rotation of engine 1 thus corresponds to an intendeddirection of rotation provided for safe operation of engine 1.

If, however, piston 2 moves upward, i.e., in the wrong direction, thepositions of inlet valve 5 and outlet valve 6 being the same, anoverpressure prevails in inlet channel 7, i.e., a pressure that ishigher than that in outlet channel 8. Consequently, the exhaust gasesfrom the combustion do not escape through outlet valve 6, but throughopen inlet valve 5 into inlet channel 7 and may damage or even destroythe components situated in inlet channel 7. It is then determined, bycomparing in control unit 12 the pressure values determined by pressuremeasuring devices 13 a and 19, that engine 1 is rotating in the wrongdirection.

This is accomplished on the basis of the fact that the pressure, whichis determined using pressure measuring device 13 a, is now higher thanthe value determined by pressure measuring device 19 in outlet channel8. It must be noted here, however, that throttling device 11 should beclosed for measuring the pressure in inlet channel 7. Only afterthrottling device 11 is closed by control unit 12 are the pressuresprevailing in inlet channel 7 and outlet channel 8 determined after apredefinable measuring period and compared.

If the pressure determined in inlet channel 7 is higher than thepressure determined correspondingly in outlet channel 8, the directionof rotation is opposite to that provided for safe operation. If thepressure determined in inlet channel 7 is lower than or equal to thatdetermined correspondingly in outlet channel 8, the instantaneousdirection of rotation corresponds to that provided for safe operation ofpiston engine 1.

In particular, a maximum value Pmax, which is not exceeded in the eventof a direction of rotation provided for safe operation of piston engine1, may be specified for the pressure prevailing in inlet channel 7 whenthrottling device 11 is closed, prior to determining the direction ofrotation.

In summary, when throttling device 11 is closed and a rotary motion hasbeen detected, the pressure prevailing in inlet channel 7 or incombustion chamber 4 is measured after a predefinable measuring periodand compared with a threshold value. If the pressure prevailing in inletchannel 7 or combustion chamber 4 is an underpressure (measuredpressure<threshold value), the direction of rotation of engine 1 iscorrect. However, if an overpressure prevails in inlet channel 7(measured pressure≧threshold value), this indicates a wrong direction ofrotation. The instantaneous pressure prevailing in outlet channel 8, inparticular, or a maximum engine type-dependent pressure value Pmaxdetermined prior to detecting the direction of rotation may be used as athreshold value. The pressure prevailing in outlet channel 8 may beapproximated by modeling by simply forming the sum of the ambientpressure and the exhaust gas counterpressure.

FIG. 2 shows another piston engine as internal combustion engine 1,having a control unit 12 for determining the direction of rotation ofengine 1. This embodiment is based on a previously determined maximumvalue Pmax. Therefore, pressure measuring device 19 in outlet channel 8is omitted here. In addition, pressure measuring device 13 b is adigital pressure switch 13 b, which measures the pressure and, above apreviously determined engine-specific maximum value Pmax which describesthe maximum expected pressure in inlet channel 7 when a rotary motionhas been detected and throttling device 11 is closed, relays a signalvia line 14 to control unit 12, from which control unit 12 is able torecognize that the direction of rotation of engine 1 is wrong.

Maximum value Pmax is stored in a memory element 20 of control unit 12.Memory element 20 is a random-access memory (RAM), a read-only memory(ROM), or a flash memory, for example. A computer program, used forcarrying out the exemplary method according to the present inventionwhen running on a computer 21, in particular a microprocessor, is alsostored in memory element 20. The computer program is run after beingtransmitted from memory element 20 to computer 21 via data line 22either section by section or instruction by instruction or as a whole.The data line is a bus system, for example. Switch 13 b may be anelectromagnetic switch, for example, whose opening pressure may beestablished as a function of the intensity of a current applied to itselectromagnet. The intensity of the current applied may be determined asa function of value Pmax stored in memory element 20, and transmitted toswitch 13 b via line 14.

FIG. 3 shows a flow chart of the exemplary method of the presentinvention. This method is advantageously carried out or performed duringthe first rotary motions upon start of the piston engine fromstandstill. The rotational speed of the piston engine is measured in afirst step S1. A query step S2 checks whether rotational speed>0, i.e.,whether the piston engine is rotating. If this is not the case, theprocedure jumps back to step S1 and the sequence is repeated from thisposition. If a rotary motion is detected, a step S3 causes throttlingdevice 11 to close and a subsequent query step checks whether apredefinable measuring period has elapsed. The predefinable measuringperiod is selected such that it permits a reliably diagnosable pressureto be established in inlet channel 7. In a step S4, pressure sensor 13 aor 13 b then measures pressure Pin in inlet channel 7 of the pistonengine.

Subsequently a threshold value SW is determined in a step S5. It iseither already available in memory element 20 of control unit 12 asengine type-dependent maximum value Pmax or is determined, for example,by measuring pressure Pa in outlet channel 8 of the piston engine usinga pressure sensor 19 or by forming the sum of a measured ambientpressure Pu with a modeled exhaust gas counterpressure Pg. A query stepS6 compares pressure Pin determined in step S4 with threshold value SWdetermined in step S5. If pressure Pin measured in inlet channel 7 islower than threshold value SW, a step S7 determines that the directionof rotation of the piston engine is correct, and the method isterminated.

However, if query step S6 determines that the measured pressure Pin ishigher than threshold value SW, the procedure branches off to a step S8,in which it is determined that the direction of rotation is wrong.Subsequently the procedure branches off to a step S9, wherecountermeasures, such as shut-off of the ignition system or blocking ofthe fuel supply, are initiated, whereupon the method is terminated.

The exemplary method according to the present invention may prevent thepiston engine from starting in the wrong direction of rotation. This isparticularly important in the case of internal combustion engines whichare started without an electric starter or starter-generator, i.e., bythemselves by filling one or more cylinders of the engine with fuel andsubsequent controlled ignition of the fuel-air mixture. In particular,direct-injection engines may be started in this way.

1. A device for detecting the rotation direction of a piston engine,which includes at least one cylinder, a piston movable back and forth inthe cylinder, a cylinder chamber formed inside the cylinder which isdelimited by an inner cylinder wall and the piston, an inlet channelwhich opens into the cylinder chamber via at least one inlet valve, anoutlet channel which opens into the cylinder chamber via at least oneoutlet valve, at least one triggerable throttling device situated in theinlet channel, the device comprising: a control arrangement to controlthe piston engine; a measuring arrangement to measure a rotationalspeed; a triggering arrangement to trigger the throttling device; and ameasuring arrangement to measure a pressure in the inlet channel whenthe inlet valve is open and the throttling device is closed; wherein thecontrol arrangement causes the throttling device to close when a rotarymotion is detected, measures a pressure in the inlet channel after apredefinable measuring period, compares the measured pressure with apredefinable threshold value to provide a comparison result, anddetermines the rotation direction of the piston engine based on thecomparison result.
 2. The device of claim 1, wherein the device includesa pressure measuring arrangement to measure a pressure in the outletchannel.
 3. The device of claim 1, wherein the device includes amodeling arrangement to model an exhaust gas counterpressure and anambient pressure measuring arrangement to measure an ambient pressure.4. The device of claim 1, wherein the control arrangement includes amemory arrangement to store a maximum pressure specific to the pistonengine.
 5. The device of claim 1, wherein a pressure measuringarrangement in the inlet channel includes a digital pressure switchwhich triggers a switching operation when the pressure exceeds or dropsbelow the threshold value.
 6. A control system for controlling a pistonengine, which includes at least one cylinder, a piston movable back andforth in the cylinder, a cylinder chamber formed inside the cylinderwhich is delimited by an inner cylinder wall and the piston, an inletchannel which opens into the cylinder chamber via at least one inletvalve, an outlet channel which opens into the cylinder chamber via atleast one outlet valve, at least one triggerable throttling devicesituated in the inlet channel, the control arrangement comprising: adetecting arrangement to detect a rotary motion of the piston engine; acontrol arrangement to control a position of the throttling device, andto close, when a rotary motion of the piston engine is detected, thethrottling device, to measure a pressure in the inlet channel after apredefinable measuring period, to compare the pressure with apredefinable threshold value and provide a comparison result, and todetermine a rotation direction of the piston engine based on thecomparison result.
 7. A computer program executable on a processorarrangement, comprising: computer program code for detecting a rotationdirection of a piston engine, which includes at least one cylinder, apiston movable back and forth in the cylinder, a cylinder chamber formedinside the cylinder which is delimited by an inner cylinder wall and thepiston, an inlet channel which opens into the cylinder chamber via atleast one inlet valve, an outlet channel which opens into the cylinderchamber via at least one outlet valve, and t least one triggerablethrottling device situated in the inlet channel, by performing thefollowing: measuring a pressure prevailing in the inlet channel when theinlet valve is open; comparing the measured pressure with a predefinablethreshold value to provide a comparison result; and determining therotation direction of the piston engine based on the comparison result;wherein the throttling device is closed at least for a time that thepressure is measured.
 8. A computer memory medium having a computerprogram executable on a processor arrangement, comprising: computerprogram code for detecting a rotation direction of a piston engine,which includes at least one cylinder, a piston movable back and forth inthe cylinder, a cylinder chamber formed inside the cylinder which isdelimited by an inner cylinder wall and the piston, an inlet channelwhich opens into the cylinder chamber via at least one inlet valve, anoutlet channel which opens into the cylinder chamber via at least oneoutlet valve, and t least one triggerable throttling device situated inthe inlet channel, by performing the following: measuring a pressureprevailing in the inlet channel when the inlet valve is open; comparingthe measured pressure with a predefinable threshold value to provide acomparison result; and determining the rotation direction of the pistonengine based on the comparison result; wherein the throttling device isclosed at least for a time that the pressure is measured.
 9. Thecomputer memory medium of claim 8, wherein the memory medium includesone of a random-access memory, a read-only memory, and a flash memory.10. A method for detecting a rotation direction of a piston engine,which includes at least one cylinder, a piston movable back and forth inthe cylinder, a cylinder chamber formed inside the cylinder which isdelimited by an inner cylinder wall and the piston, an inlet channelwhich opens into the cylinder chamber via at least one inlet valve, anoutlet channel which opens into the cylinder chamber via at least oneoutlet valve, and t least one triggerable throttling device situated inthe inlet channel, the method comprising: measuring a pressureprevailing in the inlet channel when the inlet valve is open; comparingthe measured pressure with a predefinable threshold value to provide acomparison result; and determining the rotation direction of the pistonengine based on the comparison result; wherein the throttling device isclosed at least for a time that the pressure is measured.
 11. The methodof claim 10, wherein the threshold value is determined as a function ofa pressure prevailing in the outlet channel.
 12. The method of claim 10,wherein the piston engine is an internal combustion engine, and whereinthe threshold value is determined as a function of an ambient pressureand an exhaust gas counterpressure.
 13. The method of claim 10, whereinthe threshold value is described by a predefinable maximum pressurespecific to the piston engine.